Halosphaera

Ultrastructure

The motile cells are covered with up to four layers of submicroscopic scales
made of polysaccharides. Differences in scale structure separate
Halosphaera species from each other and from species of
Pyramimonas.

The flagellate cell cytoskeleton is based on an asymmetrical array of four
flagellar bases and four microtubular roots. One of these roots is
expanded into a layer ("spline") of ca. 20 microtubules.

At the anterior end of this root, next to the flagellar base from which
it emerges, a complexproteinaceous structure ("multilayered structure")
is present.

The overall cytoskeleton suggests the symmetrical arrangement present in
"chlorophyte" green algae such as
Chlamydomonas. However, the
"spline-MLS" system suggests the cytoskeleton present in "charophyte" green
algae and the land plants.

Also associated with the spline is the aperture of a duct system that extends
from the flagellar pit to the posterior end of the cell. It has been
suggested that this duct functions to capture food for the cell
("phagotrophy") - making Halosphaera one of the two green plants
known that is phagotrophic at the cellular level (the other is the closely
related Cymbomonas).